1. Field of the Invention
This invention relates to a cylinder liner for an internal combustion engine and a method for manufacturing the same.
2. Description of the Related Art
As a specific requirement for the internal combustion engine in recent years, there are requirements to get a long life and a low air pollution in addition to the conventional requirements of a high-speed operation and a high output.
Since an improvement over an output of the engine is accommodated by setting a super-charger, a piston ring and a cylinder liner are required to have a more anti-scuffing characteristic. In turn, as for the requirement of a low air pollution, there is increasingly required to apply an EGR, so that an anti-corrosion characteristic is required more.
In addition, in case that a long life of the engine is to be attained, a countermeasure against a cavitation at a jacket of an outer peripheral surface in the cylinder liner has become more important in addition to an improvement of anti-wear characteristic of the piston ring and the cylinder liner.
A cylinder liner applied a Tufftride treatment has been used due to the fact that there is a certain limitation only with an improvement of the cylinder liner material against the requirements of anti-scuffing, anti-corrosion and anti-wearing characteristics.
However, a nitriding treatment including a Tufftride treatment may not provide any countermeasure against the cavitation at the outer peripheral surface of the cylinder liner. In turn, as the anti-cavitation treatment performed at the outer peripheral surface, it is well known in the art to apply a hard chromium plating and this treatment is actually applied in some cylinder liners to show a certain effect.
Accordingly, there may be considered to get a cylinder liner of which outer peripheral surface is plated with hard chromium and of which inner peripheral surface is nitrided. However, if the nitriding treatment is applied after performing the hard chromium plating, a certain crack may be occurred in the hard chromium plating film to cause a hardness of the hard chromium film to be reduced, so that the cylinder liner made by this manufacturing method may not provide a sufficient anti-cavitation performance. In case that a hard chromium plating is applied after a nitriding treatment, a surplus step is added to a pre-plating process and an expenditure increases due to the fact that a close fitness of the hard chromium plating film on the nitrided layer in the outer peripheral surface and a throwing power are not well attained.